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Fleischer SM, Ross MP, Venkateswara K, Hagedorn CA, Shaw EA, Swanson E, Heckel BR, Gundlach JH. A cryogenic torsion balance using a liquid-cryogen free, ultra-low vibration cryostat. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:064505. [PMID: 35777998 DOI: 10.1063/5.0089933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 06/06/2022] [Indexed: 06/15/2023]
Abstract
We describe a liquid-cryogen free cryostat with ultra-low vibration levels, which allows for continuous operation of a torsion balance at cryogenic temperatures. The apparatus uses a commercially available two-stage pulse-tube cooler and passive vibration isolation. The torsion balance exhibits torque noise levels lower than room temperature thermal noise by a factor of about four in the frequency range of 3-10 mHz, limited by residual seismic motion and by radiative heating of the pendulum body. In addition to lowering thermal noise below room-temperature limits, the low-temperature environment enables novel torsion balance experiments. Currently, the maximum duration of a continuous measurement run is limited by accumulation of cryogenic surface contamination on the optical elements inside the cryostat.
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Affiliation(s)
- S M Fleischer
- Department of Physics and Astronomy, Western Washington University, Bellingham, Washington 98225, USA
| | - M P Ross
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - K Venkateswara
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - C A Hagedorn
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - E A Shaw
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - E Swanson
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - B R Heckel
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
| | - J H Gundlach
- Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, Washington 98195, USA
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Abstract
The space gravitational wave detection and drag free control requires the micro-thruster to have ultra-low thrust noise within 0.1 mHz–0.1 Hz, which brings a great challenge to calibration on the ground because it is impossible to shield any spurious couplings due to the asymmetry of torsion balance. Most thrusters dissipate heat during the test, making the rotation axis tilt and components undergo thermal drift, which is hysteretic and asymmetric for micro-Newton thrust measurement. With reference to LISA’s research and coming up with ideas inspired from proportional-integral-derivative (PID) control and multi-timescale (MTS), this paper proposes to expand the state space of temperature to be applied on the thrust prediction based on fine tree regression (FTR) and to subtract the thermal noise filtered by transfer function fitted with z-domain vector fitting (ZDVF). The results show that thrust variation of diurnal asymmetry in temperature is decoupled from 24 μN/Hz1/2 to 4.9 μN/Hz1/2 at 0.11 mHz. Additionally, 1 μN square wave modulation of electrostatic force is extracted from the ambiguous thermal drift background of positive temperature coefficient (PTC) heater. The PID-FTR validation is performed with experimental data in thermal noise decoupling, which can guide the design of thermal control and be extended to other physical quantities for noise decoupling.
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